Revert "Replace deprecated QSet::toList and QSet::fromList()"

Authored by hindenburg on Mar 28 2020, 6:39 PM.

Description

Revert "Replace deprecated QSet::toList and QSet::fromList()"

These are only in Qt5.14+; Konsole will be on Qt5.12 for LTS
for another year.

This reverts commit c07210056cea7b69102f51952da32928d5c8ba96.